Winter upgrade

Anything related to Lambrettas... ask tech questions, post helpful info, or just read and learn.
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dapper
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Sat Nov 20, 2021 10:53 am

Winter upgrade. So installing a AF 5 speed gearbox in the next few days. Have all the instructions downloaded. Existing gearbox stripped and noticed scoring on the top plate of the AF cassette clutch I have fitted. Will do the usual engineers blue on surfaces to try to see where the scoring is coming from (no obvious signs as yet), but just in case I'm thinking of getting a thicker chain case gasket. I've done a search on here and found no info. Anyone know who sells the thicker cork ones that I've read about somewhere?

Also, have a ScootRS (yes good old Randall) Atomic reed valve still in its box from a few years back. Running a Ron Moss Avanti top end and thinking of putting this reed valve on. I tried it against an old cast 200 cc cylinder I have lying around and it fits the inlet studs without fouling on any fins, but this may be different on the Avanti.
So I know I need to cut windows in the piston and possibly take a bit off the piston skirt on the exhaust side, so how do I measure these?

I get a lot of spitback on the Avanti as it is and thought that the reed may improve the situation and improve fuel consumption.
Anyone can point me at a good link to how to do this? Thank you.
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Warkton Tornado No.1
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Sat Nov 20, 2021 1:34 pm

Reference the crankcase cover gasket, CamLam used to sell them in about 2 mm, - I think - but there is also this:

https://www.lambrettaupgrades.co.uk/app ... ow/6507383

it's the kind of thing we tend to buy with extras as spares, so worth shopping around IMHO.

As for the spit back, have you spoken to Ron about it?

Reed valves are great devices but my belief is that they should be as close to the bore as possible. In other words, 'designed in'

Spit back caused by inlet duration can be reigned in via longer piston skirts on the inlet side &/or longer strokes, either of which may not be practicable for you. However, although I have adopted such measure with a Rapido cylinder (71 x 61) the best thing is to fit air filtration. Admittedly, any elbow needs to be H U G E to ensure flow, but it can be done, ensuring increased economy, engine longevity & your loon pants staying clean & fresh on the left leg. It's not worth doing, though, if you run a PH series carburettor - unless you enjoy 'hot flooding issues' - or any that has no float bowl overflow. The PH round slide may even exasperate spit back, for all I know......

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dapper
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Sun Nov 21, 2021 1:21 am

Thanks for the Link to Chiggy's site. Didn't know he did so much gear as that. Remember he did suspension upgrades, but he's moved on a bit. Have ordered some bits to assist with progress. Would still like to progress with the reed valve else it will sit on the shelf till kingdom come. A link to how to measure window positions would be good.
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Warkton Tornado No.1
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Sun Nov 21, 2021 5:08 am

dapper wrote:
Sun Nov 21, 2021 1:21 am
A link to how to measure window positions would be good.
I'm not aware of a link. I have an image of a piston I modified (for the type of reed valve manifold you have) in Dropbox, but given up trying to get it to transfer....Sorry :roll:

Warkton Tornado No.1
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Mon Nov 22, 2021 12:05 pm

dapper wrote:
Sun Nov 21, 2021 1:21 am
A link to how to measure window positions would be good.
I tried again & when I click on the link, I can see the image. Hopefully, so can you....

https://www.dropbox.com/preview/Piston% ... nifold.jpg

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dapper
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Mon Nov 22, 2021 5:58 pm

Thanks for trying. I tried the link as I do have Dropbox, but a banner came up saying unavailable. However, I did come across this on You Tube from Piston Ported in the states,( https://www.youtube.com/watch?v=1L8x6UCgwMI ) which is helpful except he doesn't explain how he came cross his measurements from piston crown to top of window or from piston skirt up (unless he's just saying he copied the Imola, which is fine for him but no good to anyone else) and there must be a way of measuring how much to take off on the exhaust side of the skirt. I understand that its all dependant on port opening degrees, but there must be some methodology.
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dapper
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Mon Nov 22, 2021 6:01 pm

Oh, and on another of his YT vids ( https://www.youtube.com/watch?v=puRSF70RVTc ) there is this very handy tool for holding the layshaft tight for pulling it in to the rear hub bearing, which I'm going to have a go at making. Think someone over here was making them but they seem to have stopped for some reason.
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dapper
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Mon Nov 22, 2021 6:06 pm

And finally this one with a very easy to make rear hub holding tool for tightening up the rear hub nut. Cheap to make and carry in your legshield tool box and much more convenient on the road that half a split rim welded to some angle iron
https://www.youtube.com/watch?v=EMsmUA9MJKE
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dapper
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Mon Nov 22, 2021 6:16 pm

dapper wrote:
Mon Nov 22, 2021 6:01 pm
Oh, and on another of his YT vids ( https://www.youtube.com/watch?v=puRSF70RVTc ) there is this very handy tool for holding the layshaft tight for pulling it in to the rear hub bearing, which I'm going to have a go at making. Think someone over here was making them but they seem to have stopped for some reason. Although I don't personally condone his use of the rear sprocket in his method.
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Warkton Tornado No.1
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Mon Nov 22, 2021 6:34 pm

dapper wrote:
Mon Nov 22, 2021 5:58 pm
Thanks for trying. I tried the link as I do have Dropbox, but a banner came up saying unavailable. However, I did come across this on You Tube from Piston Ported in the states,( https://www.youtube.com/watch?v=1L8x6UCgwMI ) which is helpful except he doesn't explain how he came cross his measurements from piston crown to top of window or from piston skirt up (unless he's just saying he copied the Imola, which is fine for him but no good to anyone else) and there must be a way of measuring how much to take off on the exhaust side of the skirt. I understand that its all dependant on port opening degrees, but there must be some methodology.
If you look on this Forum about the subject of posting images, you will see that there is a lot of negative history associated with it.......

I will look @ the various videos when time allows, thank you. Meanwhile.....If you want to PM me an email address I will be able to hit the share option, so @ least you will be able to see it.

It's a photo I took with some dimensions added. Hopefully it will give you the confidence to make the alterations to your piston, because until any of us have done so, we're flying blind to an extent.

What i try to do is ensure best engineering practice as far as retaining strength whilst making sure the port is adequate. Consequently, the surface finish of the modifications are polished & large fillets are employed. I cannot see the point in just drilling two holes either side of the conrod's active area because, after all, as soon as any hole goes in then the reliance upon the reed's function is total.

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